Applied class/data-attribute naming convention to icon-slide buttons.

Following up on https://github.com/h5bp/Effeckt.css/issues/147 :

I've tried to apply the proposed class/data-attribute naming conventions to the sliding icon buttons. So the button markup looks like this:

```html
<button class="effeckt-button" data-effeckt-type="icon-slide from-top">
  <span class="effeckt-button-label user-designated-icon">Icon from top</span>
</button>
```

For demo purposes, I have the effect run on hover -- but the SCSS could be easily altered so that the effect runs when JS applies `data-effeckt-state="active"`.